Image converter and method and apparatus for producing the same



March 14, 1961 D. w. DAVIS 2,975

IMAGE CONVERTER AND METHOD AND APPARATUS FOR PRODUCING THE SAME 2 Sheets-Sheet 1 Filed July 17, 1958 INVENTQR. Dean [M Dav/s Arte/v2 e ys March 14, 1961 D. w. DAVIS IMAGE CONVERTER AND METHOD AND APPARATUS FOR PRODUCING THE SAME Filed July 17, 1958 2 Sheets-Sheet 2 INVENTOR. Dean W. Dav/'5 A rte/ways United States Patent MAGE CONVERTER AND METHOD AND APPA- RATUS FOR PRODUCING THE SAME Dean W. Davis, Fort Wayne, Ind., assignor to International Telephone & Telegraph Corporation Filed July 17, 1958, Ser. No. 749,241

15 Claims. (Cl. 316-49) The present invention relates to an image converter and method and apparatus for producing the same, and more particularly to an electron discharge type of image converter of small thickness dimension and having a minimum of spacing between the cathode and anode.

Image converters of the type which employ evacuated envelopes may be functionally characterized as fitting into one of two general types of construction: (1) those requiring focusing of the electron beam and ('2) those not requiring focusing of the electron beam. All of such tubes employ a photoelectric cathode which 'is spaced from a phosphor anode, the cathode upon receiving radiant energy emitting an electron beam and the phosphor anode receiving this beam and luminescing accordingly. In the first category mentioned above, the cathode and anode are spaced so far apart that either electrostatic or magnetic focusing elements are 'required for focusing the electrons emitted by the cathode" onto the anode. Such constructions are well known, one type of such construction being disclosed and claimed in Day Patent #2,708,250, issued May 10, 1955, and entitled Tube Assembly. The tubes or devices falling in the second category differ primarily in the fact that the cathode and anode are disposed immediatelyadjacent to each other such that electrons almost immediately after being emitted by the cathode impinge the anode. In this type of construction, no electrostatic or magnetic focusing is required. Thus, the constructions of the two different categories may be simply characterized as being thick" or thin," the thick tube requiring some kind of focusing and the thin tubes requiring none. A typical thin tube is disclosed in Bitner Patent #2,120,916. Since the cathode must be photoelectric (that is, must emit electrons in response to radiant energy excitation) it is necessary that the cathode be formed in a vacuum. This means, then, that the cathode is usually formed as-the last step in the manufacturing process, suitable cathodeforming means and materials being included within the tube envelope. Following this cathode-forming step, the envelope is sealed off and the tube is then essentially completed.

Such photoelectric cathodes usually comprise silveroxide-cesium, and unless the formation of this cathode is strictly controlled, contamination of the other tube parts will result, thereby impairing tube operation. "For a disclosure as to a method and apparatus for forming such cathodes, reference is made to Lindsay application Serial No. 404,699, filed Jan. 18, 1954, now Patent No. 2,870,315 issued January 20, 1959. When the cathode and anode are spaced far apart, it is possible to form the cathode without unduly contaminating the other tube parts method and apparatus Patented Mar. 14, 1961 By means of the present invention, it is possible to fabricate an image converter of only negligible thickness with out encountering the usual difiiculties connected with formation of the photoelectric cathode in tubes of thin design.

It is therefore an object of this invention to provide a for fabricating an extremely thin image converter.

It is another object of this invention to provide an ext'remely thin image converter wherein contamination of the tube parts is held to a minimum or is substantially eliminated. p

It is still another object of this invention to provide an apparatus for fabricating an extremely thin image conand to obtain uniform sensitivity across the cathode surface. However, when the cathode and anode are close together, it has been found to be quite difficult, and in some cases impossible, to fabricate properly the cathode, such close spacing resulting in non-uniformity of sensitivity over the cathode area. 3

verter, which apparatus is useful in the formation of the photoelectric cathode while the cathode and anode elements are spaced relatively far apart but permit these two elements to be positioned and secured immediately adjacent to each other without destroying the vacuum condition required during cathode formation.

It is yet another object of this invention to provide a method for facribating an extremely thin 'nnage converter wherein the photoelectric cathode is formed on a surface which is spaced relatively far distant from the anode but following which the anode may be positioned immediately adjacent the formed cathode, all of these operationsbeing performed in a substantial vacuum.

. According to the present invention, the method of fabricating a thin image converter having an anode and a cathode positioned immediately adjacent to each other comprises the steps of positioning ananode supporting element and a cathode supporting element a predetermined distance apart, evacuating the space between such supporting elements, forming a photocathode on one of said supporting elements, moving said elements toward each other while the space therebetween is evacuated until such elements are a second predetermined distance apart, hermetically securing said elements in position at said second predetermined distance, thereby removing the excess volume from the tube.

The apparatus of this invention used in fabricating the thin image converter comprises a supporting plate, a

first tubular elements secured at one end to the support ing plate, a first phosphor-supporting electrode secured secured at one end to the other end of the envelope, and

a cathode-supporting electrode mounted on the remaining 5 end of the second tubular element, thefirstand s econd tubular elements having mating portions which are en-* gageable when the envelope is collapsed for moving the tubular elements together. The extremely thin image converter of this invention the other plate, the envelope being metal and having;aconductive connection with only one of theelements, the

other element being insulated from said envelope, andla I terminal connected to the other element.

. The above-mentioned and other features and objects. of this invention and the manner of attaining them willlbe come more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. l is a longitudinal sectional illustration of one apparatus embodiment of this invention;-

Fig. 2 is a similar sectional view illustrating additional apparatus used in fabricating the thin image converter; Fig. 3 is a longitudinal sectional view showing the image converter as being essentially completed and the.

apparatus in condition for separation from the finished converter; and

Fig. 4 is a side view of one of the split rings illustrated in section in Fig. 1.

Referring to the drawings, the apparatus of this invention is shown as comprising a flat, relatively thick metal supporting plate 1 having an access opening 2. On this plate 1 and in substantial alignment with the access opening 2 is mounted and hermetically sealed a metal sleeve 3 having a stepped diameter portion 4 on its left-hand end. A radial shoulder 5 connects the reduced diameter portion 4 with the sleeve proper. An inwardly turned, annular fiange 6 is formed on the end of the reduced diameter portion 4.

This sleeve 3 preferably is formed of Kovar, and has sealed on the inturned flange 6 a substantially fiat, discshaped, transparent support or faceplate 7. The material of this faceplate 7 may be glass of the type having suitable sealing characteristics with the sleeve 3.

On the left-hand face of this faceplate 7 is a layer 8 of aluminized phosphor, this layer terminating just short of the flange 6 so as to be insulated therefrom. A suitable terminal or connecting lead 9 passes through the faceplate 7 and connects to the aluminized phosphor layer 3. This phosphor layer is fabricated in accordance with the usual methods and techniques employed in fabricating the display screen of aluminized cathode ray tubes and in the finished image converter constitutes the anode element.

Surrounding the sleeve 3 and hermetically sealed to the supporting plate 1 is a collapsible or bellows-type envelope 10 of conventional construction. Such envelopes are commonly used in vacuum technology for introducing motion to parts situated inside an evacuated container from the outside thereof, and are formed of metal having suflicient strength to permit the space inside the envelope to be evacuated-without radially collapsing. By reason of the bellows or accordion type construction, the envelope is free to extend and collapse axially. The natural resilience in the material of the envelope tends to hold it in the illustrated extended position.

n the left-hand end of the envelope 10 is welded or otherwise hermetically secured a second Kovar sleeve or ring 11 having a reduced diameter portion 12 and, an interconnecting radial shoulder 13. An inturned lip 14. on the end of the reduced diameter portion 12 supports a glass or the like cathode-supporting plate 15, the two plates 15 and 7 being stationed in substantial axial alignment as well as parallel. The inner diameter of the sleeve 11 is made to substantially coincide with the outer diameter of the sleeve 3. Similarly, the inner diameter of the reduced portion 12 is substantially coextensive with the outer diameter of the other reduced portion 4. The shoulders 13 and of the two sleeves are engageable with each other in the finished tube, as illustrated in Fig. 3.

An exhaust tubulation 16 communicates with the inte rior of the envelope through a suitable opening 17 in the supporting plate 1. One or more beads of silver 18 are supported inside the envelope 10 by means of two wires or electrode members 19 connected to opposite sides of the bead. These electrodes 19 pass through the supporting plate 1 and are insulated from the latter by a suitable glass or the like feed-through insulators 20.

A metal channel (not shown) of cesium-containing compounds for distillation of cesium when heated by passing a current through the channel as is well known is similarly supported inside the envelope 10 at a point circumferentially spaced from the silver beads 18. The beads and channel are used in forming the cathode on the inner surface of the faceplate 15.

In the outwardly opening folds of the envelope 10 are positioned a series of annular spacers or rings 21 (see Fig. 4) formed in semicircular sections which are separable. These spacers are loosely positioned in the companion folds and normally will fall therefrom, but when the interior of the envelope 10 is evacuated, the envelope collapses onto the spacers and thereby holds them in place. Such spacers serve to prevent complete collapse of the envelope.

Having now described the principal portions of the apparatus used in fabricating the image converter of this invention, the operation thereof as well as the steps of the method will now be described. With the apparatus assembled as illustrated in Fig. 1, and a suitable vacuum or exhausting pump (not shown) operatively connected to the tubulation 16, the envelope 10 is evacuated. As explained before, the spacers 21 prevent the envelope 10 from completely collapsing. Also, the spacers 21 are held in place by the force of the bellows thereagainst. At this stage of processing, the faceplate 15 has been previously thoroughly cleaned and is free of dust and other foreign material. As the first step in forming the photoelectric cathode on the inner surface of this faceplate 15, a silver film of minute, substantially transparent thickness is evaporated onto the faceplate from the silver beads 18 through which a vaporizing current is passed by means of the electrodes 19. Next, a measured quantity of pure oxygen is admitted to the interior of the tube through the tubulation 16 for oxidizing the silver film. In accordance with conventional practice, this oxidation is expedited and made more complete by producing a glow discharge in the oxygen by means of, for example, a radio frequency field positioned adjacent to faceplate 15. Upon completion of this oxidation step, the excess oxygen is pumped out of the tube through the tubulation 16.

At this stage of processing, the tube is ready for applying the cesium onto the silver oxide base. In the present instance, a channel supported as previously explained by electrodes similar to those indicated by the numeral 19 and containing cesium chromate and pure silicon is heated by passing an electrical current therethrough. As a result of this heating, pur-e cesium is released and the silicon is chemically combined with the chromate to provide a stable composition which does not interfere with the operating characteristics of the tube.

Before releasing the cesium, the temperature of the glass plate 15 is closely controlled, the method and apparatus for achieving this control being exemplified by the disclosure of Lindsay application Ser. No. 404,699, filed Jan. 18, 1954 and entitled Apparatus for Forming Cathodes.

The cathode is sensitized by further evaporation of silver thereon and by heat treatment.

After this cathode is formed, and while the envelope 10 is maintained evacuated, a bell jar 22 as shown in Fig. 2 is fitted over the tube assembly and sealed to the supporting plate 1 by means of a neoprene or the like gasket 23. A vacuum pump (not shown) is connected to the tubulation or nozzle 24 of the bell jar and thereafter operated to draw a vacuum inside the jar. Once the pressure on the outside of the envelope 10 equalizes that on the inside, the natural resiliency in the bellows causes-the envelope to expand or distend slightly, thereby releasing the spacers 21 which now fall to the bottom of the bell jar.

Following this, the vacuum pump connected to the tubulation 24 is disconnected, while the valve 25 is turned oiff The valve 25 is operated to permit air at atmospheric pressure to enter slowly the bell jar 22. thereby causing the envelope 10 to completely collapse to the position as shown in Fig. 3 This collapse of the envelope serves to telescope the sleeve member-11 over is to be recognized that by reason of the vacuum being maintained inside the envelope (by previously having sealed off the tubulation 16), the space which now exists between the contiguous faceplates is also evacuated. The two sleeves 3 and 11 arenext seam welded around the circumference thereof at about the point 26, following which the two sleeves are cut off at about the point 27 for removing the bellows and supporting plate construction. This completes the fabrication of the image converter, 1 5

As will now be apparent, the cathode formed on the faceplate will be substantially uniform throughout its area as is conventionally accomplished in the longer tubes which incorporate electron-accelerating and focusing elements. Also, the phosphor anode as wellas the final tube envelope are relatively uncontaminated by the cesium during cathode formation, thereby providing more predictable operating characteristics. An improved signal-to-noise ratio is also obtained. 7 7 While this image converter does not ordinarily employ any of the usual focusing and accelerating electrodes, a magnetic focusing yoke or coil surrounding the tube may be used if needed for a particular mode of operation.

While I have described above the principles of my invention in connection with specific apparatus, it is to'be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. The method of fabricating an electron discharge device having an anode and a cathode which are positioned closely together comprising the steps of positioning an anode supporting element and a cathode supporting element a substantial distance apart, evacuating the space between said supporting elements, forming a photocathode on one of said supporting elements,,next moving said elements toward each other while said space is evacuated until they are positioned in close proximity, securing said elements in said close proximity, and hermetically sealing the space between said elements.

2. The method of fabricating an electron discharge device having an anode and a cathode which are positioned closely together comprising the steps of positioning an anode supporting element and a cathode supporting element a substantial distance apart, evacuating the space between said supporting elements, forming a layer of silver oxide on one of said supporting elements, reacting cesium with said silver oxide to obtain a photosensitive cathode, next moving said elements toward each other while said space is evacuated until they are positioned in close proximity, securing said elements in said close proximity, and hermetically sealing the space between said elements. p 3. The method of fabricating an electron discharge device having anode and cathode supporting elements joined to opposite ends of a vacuum-tight collapsible envelope comprising the steps of separating said elements a substantial distance apart, evacuating said envelope while said elements are so spaced apart, forming a photocathode on one of said elements, collapsing said envelope to move said elements into close proximity to each other, securing said elements in the collapsed position of said envelope, and hermetically sealing the space between said elements.

4. The method of fabricating an electron discharge device having anode and cathode supporting elements joined to opposite ends of a vacuum-tight collapsible envelope comprising the steps of separating said elements asubstantial distance apart, evacuating said envelope while said elements are so spaced apart, forming aphotocathode on one of said elements, collapsing said envelope to move said elements into close proximityto each other, forming a second rigid envelope around said elements in the collapsed position of said collapsible envelope, and hermetically sealing the second envelope.

5. The method of fabricating an electron discharge' device having anode and cathode supporting elements joined to opposite ends of a vacuum-tight collapsible envelope comprising the steps of separating said elements a substantial distance apart, evacuating said envelope while said elements are so spaced apart, forming a photocathode on' one of said elements, collapsing said envelope to move said elements into close proximity to' each other, "forming a second rigid envelope around said elements in the collapsed position of said collapsible envelope, hermetically sealing the second envelope, and

then removing the collapsible envelope without disturbing the vacuum condition inside the second envelope.

6. Apparatus for use in fabricating an electron discharge device comprising a first electrode, a second electrode spaced from said first electrode, a vacuum-tight collapsible envelope including elements operatively connecting opposite ends of said envelope to said electrode so that said envelope surrounds the space between said first and second electrodes, said envelope being evacuated and operable to move said electrodes toward and away from each other, said elements having mating portions forming a second envelope surrounding the space between said electrodes when the latter are moved toward each other to a position in close proximity.

7. Apparatus for use in fabricating an electron discharge device comprising a first electrode, a second elec: trode spaced from said first electrode, a vacuum-tight collapsible envelope including elements operatively connecting opposite ends of said envelope to said electrode so that said envelope surrounds the space between said first and second electrodes, said envelope being evacuated and operable to move said electrodes toward and away from each other, said elements having mating portions forming a second envelope surrounding the space between said electrodes when the latter are moved toward each other to a position in close proximity, means hold:

ing said collapsible envelope in distended condition while I evacuated, and means selectively collapsing said collapsible envelope to move said mating portions into sealing engagement with each other.

8. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first tubular element secured at one end to said supporting plate, a first electrode secured to the other end of said element, a collapsible envelope surrounding said first tubular element and secured at one end to said supporting plate,

a second tubular element secured at one end to the other 1 i end of said envelope, and a second electrode mounted on I the remaining end of said second tubular element, said first and second tubular elements having mating portions which are engageable when said envelope is collapsed for moving said tubular elements together. I

9. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first tub u lar element securedat one end to said supporting plate, 1

a first transparent supporting member secured to the other end of said element, a layer of phosphor on' one phor layer being disposed in the space surrounded by said collapsible envelope, said first and second tubular.

elements having mating portions which are engageable gamma when said collapsible envelope is collapsed for moving said tubular elements together.

10. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first elongated sleeve having opposite ends, one of said ends being mounted on and hermetically sealed to said supporting plate, the other end having a stepped diameter portion, a first transparent supporting plate mounted on and hermetically sealed to said other end, a cylindrically shaped bellows-type envelope surrounding said sleeve and mounted on and hermetically sealed at one end to the first-mentioned supporting plate, said envelope being collapsible axially, a second elongated tubular sleeve coaxially mounted on and hermetically sealed to the remaining end of said envelope to be movable therewith, said second sleeve having a stepped diameter portion and being telescopically engageable with said first sleeve, the stepped diameter portions of both sleeves being abuttingly engageable, and a second transparent supporting plate mounted on and hermetically sealed to the stepped diameter portion of said second sleeve, said first and second transparent plates being spaced apart when said stepped diameter portions are abutted.

11. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first elongated sleeve having opposite ends, one of said ends being mounted on and hermetically sealed to said supporting plate, the other end having a stepped diameter portion, a first transparent supporting plate mounted on and hermetically sealed to said other end, a cylindrically shaped bellows-type envelope surrounding said sleeve and mounted on and hermetically sealed at one end to the first-mentioned supporting plate, said envelope being collapsible axially, a second elongated tubular sleeve coaxially mounted on and hermetically sealed to the remaining end of said envelope to be movable therewith, said second sleeve having a stepped diameter portion and being telescopically engageable with said first sleeve, the stepped diameter portions of both sleeves being abuttingly engageable, a second transparent supporting plate mounted on and hermetically sealed to the stepped diameter portion of said second sleeve, said first and second transparent plates being spaced apart when said stepped diameter portions are abutted, a layer of phosphor on the surface of said first transparent plate facing said second transparent plate, and a photoelectric cathode on the surface of said second transparent plate facing said first transparent plate.

12. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first elongated sleeve having opposite ends, one of said ends being mounted on and hermetically sealed to said supporting plate, the other end having a stepped diameter portion, a first transparent supporting plate mounted on and hermetically scaled to said other end, a cylindrically shaped bellows-type envelope surrounding said sleeve and mounted on and hermetically sealed at one end to the firstmentioned supporting plate, said envelope being collapsible axially, a second elongated tubular sleeve coaxially mounted on and hermetically sealed to the remaining end of said envelope to be movable therewith, said second sleeve being axially aligned with said first sleeve, said second-sleeve having a stepped diameter portion and being telescopically engageable with said first sleeve, the stepped diameter portions of both sleeves being abuttingly engageable, a second transparent supporting plate mounted on and hermetically sealed to the stepped diameter portion of said second sleeve, said first and second transparent plates being spaced apart when said stepped diameter portions are abutted, a layer of phosphor on the surface of said first transparent plate facing said second transparent plate, and a photoelectric cathode on the surface of said second transparent plate facing said first transparent plate.

13. Apparatus for use in fabricating an electron dis- 8 charge device comprising a supporting plate, a first elongated sleeve having opposite ends, one of said ends being mounted on and hermetically sealed to said supporting plate, the other end having a stepped diameter portion, a first transparent supporting plate mounted on and hermetically sealed to said other end, a cylindrically shaped bellows-type envelope surrounding said sleeve and mounted on and hermetically sealed at one end to the first-mentioned supporting plate, said envelope being collapsible axially, a second elongated tubular sleeve coaxially mounted on and hermetically sealed to the remaining end of said envelope to be movable therewith, 'said second sleeve having a stepped diameter portion and being telescopically engageable with said first sleeve, the stepped diameter portions of both sleeves being abuttingly engageable, a second transparent supporting plate mounted on and hermetically sealed to the stepped diameter portion of said second sleeve, said first and second transparent plates being spaced apart when said stepped diameter portions are abutted, a layer of phosphor on the surface of said first transparent plate facing said second transparent plate, and means disposed inside said envelope for forming a cathode on the inner surface of said second transparent plate.

14. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first elongated sleeve having opposite ends, one of said ends being mounted on and hermetically sealed to said supporting plate, a reduced diameter portion on the other end of said sleeve, an annular radial shoulder connecting said reduced diameter portion to said other end of said sleeve, an annular inturned flange on the end of said reduced diameter portion, said flange being immediately adjacent to said shoulder, a first transparent supporting disc fitted inside said sleeve and hermetically secured to said flange, a cylindrically shaped bellows-type envelope surrounding said sleeve and mounted on and hermetically sealed at one end to the first-mentioned supporting plate, said envelope being collapsible axially, a second elongated tubular sleeve coaxially mounted on and hermetically sealed to the remaining end of said enveope to be movable therewith, a reduced diameter portion connected to the end of said second sleeve by means of an annular shoulder, the inner diameters of said second sleeve and its reduced dizuneter portion being substantially equal to the outer diameters of said first sleeve and its reduced diameter portion, respectively, the shoulders on said two sleeves being engageable, said first and second sleeves being axially aligned, an inwardly turned lip on the end of the second reduced diameter portion, a second transparent supporting disc hermetically sealed to said lip, both of said sleeves being formed of metal, a layer of phosphor on the inner surface of the first transparent disc and spaced from said second sleeve, a terminal lead connected to said phosphor layer, said envelope being collapsible to telescope said tubular sleeves and to engage said shoulders, a plurality of split spacer rings fitted into the outwardly opening folds of said envelope for holding the latter against collapse, means for evacuating said envelope, means for forming a photoelectric cathode on the inner surface of said second transparent disc, and means for removing said rings from said envelope after said cathode has been formed.

15. Apparatus for use in fabricating an electron discharge device comprising a supporting plate, a first elongated sleeve having opposite ends, one of said ends being mounted on and hermetically sealed to said supporting plate, a reduced diameter portion on the other end of said sleeve, an annular radial shoulder connecting said reduced diameter portion to said other end of said sleeve, an annular inturned fiange on the end of said reduced diameter portion, said flange being immediately adjacent to said shoulder, a first transparent supporting disc fitted inside saidsleeve and hermetically secured to said flange, a cylindrically shaped bellows-type envelope surrounding said sleeve and mounted on and hermetically sealed at one end to the first-mentioned supporting plate, said envelope being collapsible axially, a second elongated tubular sleeve coaxially mounted on and hermetically sealed to the remaining end of said enveope to be movable therewith, a reduced diameter portion connected to the end of said second sleeve by means of an annular shoulder, the inner diameters of said second sleeve and its reduced diameter portion being substantially equal to the outer diameters of said first sleeve and its reduced diameter portion, respectively, the shoulders on said two sleeves being engageable, said first and second sleeves being axially alinged, an inwardly turned lip on the end of the second reduced diameter portion, a second transparent supporting disc hermetically sealed to said lip, both of said sleeves being formed of metal, a layer of phosphor on the inner surface of the first transparent disc and spaced from said second sleeve, a terminal lead connected to said phosphor layer, said envelope being collapsible to telescope said tubular sleeves and to engage said shoulders, a plurality of split spacerrings fitted into I the outwardly opening folds of said envelope for holding the latter against collapse, means for evacuating said envelope, means for forming a photoelectric cathode on g the inner surface of said second transparent disc, a chamber enclosing said envelope and the two transparent discs, and means for evacuating said chamber whereby said rings may be released from said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 

